1. Field of the Invention
The present invention relates to a development apparatus adopting a so-called overflow system, and particularly to a developer conveying technique.
2. Description of the Related Art
Heretofore, in a development technique to perform development processing with a two-component developer including carrier and toner, in order to prevent deterioration of image characteristics due to the peeling of a resin coat material of the surface of the carrier resulting from the consumption of the toner or the lowering of charging performance as the developer by the attachment of a toner component to the surface of the carrier, a system of supplying the toner and carrier into the development apparatus has been proposed. Specifically, there is known a method in which toner and carrier are separately supplied, or a method in which a toner cartridge to be replenished is mixed with a small amount of carrier and they are supplied to a development apparatus (see JP-A-62-127874).
Heretofore, when developer reaches the end of its life, a total replacement operation is performed, however, in this system, carrier is also supplied during a normal developing operation at the same time as the toner. Although the toner is consumed by the development, since the supplied carrier remains in a container of the development apparatus, when toner density in the development container is kept constant, the bulk of the developer is increased. In order to deal with the increase in the bulk of the developer as stated above, there is known a method in which the so-called overflow is used and the developer is discharged to the outside of the development container. Besides, there is also known a system in which a part of the developer is mechanically discharged by control, and a new developer is supplied, so that the developer in the development apparatus is replaced (see JP-A-6-301289).
As stated above, the developer which reaches the end of its life and is deteriorated is partially replaced by a new one, and the developer performance is kept, so that the number of times of collective replacement of the developer is reduced, and the maintenance property is improved.
In the development apparatus to perform the replacement of the developer as described above, there is known a technique in which in order to keep the amount of developer to be constant, bulk density is regulated as an index of the fluidity of the developer (JP-A-9-185177), however, since the developer is changed according to the use state, it is not practical. Besides, there is known a technique in which a low conveying unit of developer is provided by decreasing the diameter of a developer agitating wing or the pitch, and discharge of the developer is performed (JP-A-2000-81787).
However, in the above related art, it is impossible to deal with a change in a physical property of a developer resulting from a use condition, such as arrival to the end of its life due to deterioration or an environmental change, and there has been a case where the amount of developer can not be kept to be constant. That is, in the above related art, there is a case where the discharge of the developer is not sufficiently performed due to the change in the physical property of the developer, and it has not been sufficient for proper maintenance of the amount of the developer and for maintenance of the performance of the developer.